A thermal protection system (TPS) may include various materials in different locations of a vehicle such as a jet-propelled vehicle, an aerospace vehicle, a rocket, etc., depending on the amount of heat protection needed. For example, reinforced carbon-carbon may be used in the nose or leading wing edges of a spacecraft, such as a space shuttle. High temperature reusable surface insulating tiles may be used on the underside of an aircraft. Flexible insulation blankets, low temperature reusable surface insulating tiles, and other materials may be used for different locations on the spacecraft. Each type of thermal protection system may have specific heat protection, impact resistance, and weight characteristics.
It is desirable to have a thermal protection system that requires little or no maintenance. Some thermal protection systems may include modular components that may be quickly removed and replaced. Insulating tiles are examples of components that may be used in a thermal protection system. An insulating tile is a thermal protection system component that may be fabricated from various materials such as ceramic and/or ceramic matrix composite materials. More specifically, the insulating tile may have, for example, a ceramic substrate with a ceramic matrix composite layer wrapped around the inner core. In the event that the insulating tile may need to be replaced after being in service, it is desirable to minimize the amount of time needed to replace the insulating tiles on a vehicle, such as a spacecraft. For example, a vehicle turnaround time of around 48 hours or as little as two hours may be desirable.
Conventional thermal protection systems on existing spacecraft may be adhesively bonded or mechanically attached. With adhesively bonded thermal protection systems, the amount of time and cost associated with installation, inspection, and/or repair may be much greater compared to a mechanically attached system. Further, bonded thermal protection systems may be difficult to remove without damaging or destroying the insulating tile or the underlying substrate of the vehicle. As a result, inspection of a spacecraft substructure and/or internal spacecraft subsystems may be time consuming and expensive. Another drawback of adhesively bonded thermal protection systems is that the temperature of the substrate to which the tile is adhesively bonded may exceed the failure temperature of the adhesive, particularly in exhaust systems and other systems having a high thermal output. In these high-temperature systems, a mechanically attached thermal protection system design must be utilized.
Mechanical attachments for insulating tiles may include, for example, a standoff or a carrier panel. A standoff thermal protection system may include stiffened panels encapsulating a back face insulation that is mechanically attached through flanges or metallic standoffs. A carrier panel thermal protection system may have insulating tiles and/or blankets that are adhesively bonded to metal or composite carrier panels that are mechanically attached to a structure. While thermal protection systems using standoff panels are easier to replace than an insulating tile adhesively bonded directly to the protected substrate, they are still prone to failure at higher temperatures (e.g., >700° F.) as the insulating tile is adhesively bonded to the metal or composite carrier panel.
Mechanically attached thermal protection systems may include brackets for attaching the insulating tile to a deck or substrate using bolts positioned between adjacent insulating tiles. The use of bolts may require a greater space between adjacent insulating tiles when compared with adhesively attached insulating tiles, for example to provide access to the bolts to allow replacement of insulating tiles. While adhesive attachment may allow tighter placement of adjacent insulating tiles, adhesive is less robust in high temperature environments than some mechanical attachment techniques.
With either mechanically attached or thermally attached insulating tiles, a space or gap between adjacent insulating tiles is typically filled with a flexible thermal insulation, or gap filler, to prevent heated gases from reaching an underlying substrate or deck to which the insulating tiles are attached. A large gap between insulating tiles can be difficult to fill and may be prone to failure during heating, for example due to differences in coefficients of thermal expansion between the insulating tile and the gap filler. Further, the thermal insulation in larger spaces may be prone to accelerated deterioration with increasing inter-tile gap widths. Additionally, larger spaces may result in larger aerodynamic drag, which is typically undesirable.
Therefore, a mechanical attachment system and method that allows closer spacing of adjacent insulating tiles and high structural interface temperature, while allowing tile replacement and/or other advantages over conventional adhesive and mechanical attachment thermal protection systems, would be desirable.